Control of unwanted immune responses is critical in treating autoimmune diseases, transplant rejection, allergic diseases, and T-cell-derived cancers. The activity of overly aggressive T-cells can be contained by immunosuppression or by induction of immunological tolerance. Apoptosis is believed to be involved in maintaining proper functions of the immune system and removing unwanted cells, such as overly aggressive T-cells (Kabelitz et al. (1993) Immunol Today 14, 338-340; and Raff (1992) Nature 356, 397-399).